The present invention relates to electric machines and, in particular, to electric machines fed by an exciter.
The generation of electrical power typically includes one or more turbines. In the case of gas turbines, a compressor is coupled to a combustor that combusts a gas or fuel oil in a stream of compressed air. The combustor is coupled and provides a hot gas flow resulting from the combustion of the gas or fuel oil to a turbine portion. The turbine portion includes a rotor with attached blades. The hot gas is passed over the blades, which, in turn, causes the rotor to turn. In this manner, the energy from the hot gas is converted to rotary motion.
To generate electricity, the rotor is coupled to a generator. In this respect, the turbine rotor acts as the prime mover for the generator. Of course, other sources could act as the prime mover.
In general, a generator converts rotary motion into electricity. In more detail, a generator includes an armature and a field. The armature is the power-producing component of a generator and includes armature windings that generate the output electrical current. The armature can be on either the rotor or the stator. The field is the magnetic field component of a generator. Power transferred into the field circuit is typically much less than in the armature circuit. Accordingly, generators nearly always have the field winding on the rotor and the stator serves as the armature winding. In such a configuration, only a small amount of field current needs to be transferred to the rotor from an exciter via slip rings.
A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary structure to a rotating structure. In the case of a generator, the slip rings allow for current to be passed from an exciter to the rotor. The slip rings are coupled to the rotor and receive current from the exciter through fixed contacts or brushes held in contact with the rings.